In general, an infrared detector is adapted to detect a temperature change of an infrared detecting element caused by infrared energy impinging upon the infrared detecting element. Thus, in order to prevent the impinging infrared energy from diffusing to surrounding areas, the infrared detector defines an inner space for containing the infrared detecting element therein and the inner space is maintained in vacuum. As a technique to achieve a high degree of vacuum of the inner space of the infrared detector in a short period of time, it is known to solder a ceramic container having an infrared detecting element mounted therein to a lid member in a vacuum chamber (see Japanese Patent Application Laid-Open Publication No. 2003-139616, for example). In this technique, the ceramic container and the lid member equipped with an infrared-transmissive window member are set in respective heater devices provided to upper and lower portions of a vacuum chamber, and then closely pressed against each other while being heated by the heater devices to melt a solder material arranged on the ceramic container. Thereafter, the heating is stopped to solidify the solder material and thereby achieve an air-tightly sealed infrared detector.
The '616 publication also discloses an infrared detector wherein in order to improve the bonding strength and air-tightness between the ceramic container and the lid member, the lid member is formed with a flange surface to ensure a sufficient bonding area with the ceramic container; the ceramic container, on which the solder material is arranged, is applied with a metallization for bonding; a portion of the lid member that is to contact the solder material is surface-treated to improve an affinity for the solder material (i.e., to improve the wettability by reducing the contact angle); and an edge of the flange is beveled so as to cause the solder material to form a fillet.
Such a conventional infrared detector can be manufactured as follows: As shown in FIG. 11(a), a container-side metallization layer 96 is first formed on an upper surface of a ceramic container 94 which includes an infrared detecting element 92 contained in a cavity 93, and then, in a vacuum atmosphere, a pre-molten solder metal 99 having a melting temperature of 250° C. or lower, such as In-Sn or Sn-Ag alloys, is deposited on the container-side metallization layer 96. In this state, because the solder metal 99 has a low affinity for the ceramic container 94 (i.e., the contact angle is large and the wettability is poor) and a high affinity for the container-side metallization layer 96 (i.e., the contact angle is small and the wettability is good), the solder metal 99 stays only on the container-side metallization layer 96 due to the tension surface. Then, the ceramic container 94 is returned to an atmospheric condition, and as shown in FIG. 11(b), an unnecessary portion of the solder metal 99 as well as an oxide film formed on a surface of the solder metal 99 are cut or scraped off by means of a lathe or the like. Subsequently, the ceramic container 94 and an infrared-transmissive window member 95 formed with a window-side metallization layer 97 on its undersurface are placed at predetermined positions within a vacuum chamber and undergo a baking process for gas removal. Then, as shown in FIG. 11(c), the infrared-transmissive window member 95 is moved onto the ceramic container 94 and pressed against the ceramic container 94 in a vacuum atmosphere while being heated, and this causes the solder metal 99 and the window-side metallization 97 to be fusion-bonded to each other. Then, the temperature is lowered in the vacuum condition to solidify the solder metal 99 to seal the joint between the ceramic container 94 and the infrared-transmissive window member 95. This completes an infrared detector 1.
However, in the conventional method for manufacturing the infrared detector, the scrapped-off material may be wastefully discarded. Further, because it takes a long period of time for the baking process to complete, the metal surface exposed by scraping off the oxide film cannot be maintained clean before the sealing process. Specifically, segregation, contamination and/or dross (solder scum such as an oxide film) can appear on the solder metal surface and deteriorate the air-tightness of the solder metal. In order to improve the air-tightness, it may be conceived to oscillate the infrared-transmissive window member during the melted state of the solder metal to scrub the surface of the solder metal and thereby expose a clean surface of the solder metal anew, but this cannot completely eliminate the leakage and may still result in inferior products. Also, the above manufacturing process of the infrared detector requires a number of steps, and this can lead to a higher manufacturing cost.